Access context management for macro-level mobility management registration in an access network

ABSTRACT

In an access network which supports a mobile IP protocol, a packet data protocol context is opened at support node and a gateway node in order to establish a connection between a mobile node and a mobile IP foreign agent located at the gateway node. A mobile IP registration over the connection is initiated. The gateway node monitors whether the registration is successful or fails. The PDP context is deleted, if the registration irrecoverably fails. If the registration was unsuccessful but a retry could be successful, the PDP context may not deleted, but the registration is retried.

This is a continuation of U.S. patent application Ser. No. 10/030,538,filed on Jan. 11, 2002, which is the U.S. National Stage ofPCT/FI00/00640, filed on Jul. 11, 2000, which, in turn, relies forpriority upon Finnish Application No. 99/1597, filed on Jul. 12, 1999,the contents of all of which are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The invention relates to the management of access context in an accessnetwork, in connection with a macro-level mobility managementregistration, such as a Mobile IP registration.

BACKGROUND OF THE INVENTION

A mobile communications system refers generally to anytelecommunications system which enables wireless communication whenusers are moving within the service area of the system. A typical mobilecommunications system is a Public Land Mobile Network (PLMN). Often themobile communications network is an access network providing a user withwireless access to external networks, hosts, or services offered byspecific service providers.

The general packet radio service GPRS is a new service in the GSM system(Global System for Mobile communication). A sub network comprises anumber of packet data service nodes SN, which in this application willbe referred to as serving GPRS support nodes SGSN. Each SGSN isconnected to the GSM mobile communication network (typically to a basestation controller BSC or a base transceiver station BTS in a basestation system) so that the SGSN can provide a packet service for mobiledata terminals via several base stations, i.e. cells. An intermediatemobile communications network provides radio access and packet-switcheddata transmission between the SGSN and mobile data terminals. Differentsub networks are in turn connected to an external data network, e.g. toa public switched data network PSPDN, via GPRS gateway support nodesGGSN. The GPRS service thus allows the provision of packet datatransmission between mobile data terminals and external data networkswhen the GSM network functions as a radio access network RAN.

Third-generation mobile systems, such as Universal Mobile Communicationssystem (UMTS) and Future Public Land Mobile Telecommunications system(FPLMTS), later renamed as IMT-2000 (International MobileTelecommunication 2000), are being developed. In the UMTS architecture aUMTS terrestrial radio access network, UTRAN, consists of a set of radioaccess networks RAN (also called radio network subsystem RNS) connectedto the core network (CN). Each RAN is responsible for the resources ofits set of cells. For each connection between a mobile station MS andthe UTRAN, one RAN is a serving RAN. A RAN consists of a radio networkcontroller RNC and a multiplicity of base stations BS. One core networkwhich will use the UMTS radio access network is the GPRS.

One of the main targets in the development of mobile communicationsnetworks is to provide an IP (Internet Protocol) service with a standardIP backbone which would use a combination of mobile network mobilitymanagement in the mobile networks and Mobile IP. The basic IP conceptdoes not support the mobility of the user: the IP addresses are assignedto network interfaces depending on their physical location. In fact, thefirst field of an IP address (the NETID) is common to all interfacesthat are linked to the same Internet subnet. This scheme prevents theuser (the mobile host) from keeping its address while moving overdifferent Internet subnets, i.e. while changing the physical interface.

In order to enhance mobility in the Internet, a Mobile IP protocol forIP version 4 has been introduced by the Internet Engineering Task Force(IETF) in the standard RFC2002. A mobile IP enables the routing of IPdatagrams to mobile hosts, independently of the point of attachment inthe sub network. The mobile IP protocol introduces the following newfunctional or architectural entities.

‘A Mobile Node (MN)’ (also called Mobile Host MH) refers to a host thatchanges its point of attachment from one network or sub network toanother. A mobile node may change its location without changing its IPaddress; it may continue to communicate with other Internet nodes at anylocation using its (constant) IP address. ‘A Mobile Station (MS)’ is amobile node having a radio interface to the network. A ‘Tunnel’ is thepath followed by a datagram when it is encapsulated. The model is that,while it is encapsulated, a datagram is routed to a known decapsulationagent which decapsulates the datagram and then correctly delivers it toits ultimate destination. Each mobile node is connected to a home agentover a unique tunnel, identified by a tunnel identifier which is uniqueto a given Foreign Agent/Home Agent pair.

‘A Home Network’ is the IP network to which a user logically belongs.Physically, it can be e.g. a local area network (LAN) connected via arouter to the Internet. ‘A Home Address’ is an address that is assignedto a mobile node for an extended period of time. It may remain unchangedregardless of where the MN is attached to the Internet. Alternatively,it could be assigned from a pool of addresses.

‘A Mobility Agent’ is either a home agent or a foreign agent. ‘A HomeAgent (HA)’ is a routing entity on a mobile node's home network, whichtunnels packets for delivery to the mobile node when it is away fromhome, and maintains current location information for the mobile node. Ittunnels datagrams for delivery to, and, optionally, detunnels datagramsfrom, a mobile node when the mobile node is away from home. ‘A ForeignAgent (FA)’ refers to a routing entity in a mobile node's visitednetwork which provides routing services to the mobile node whileregistered, thus allowing a mobile node to utilize its home networkaddress. The foreign agent detunnels and delivers to the mobile nodepackets that were tunneled by the mobile node's home agent. Fordatagrams sent by a mobile node, the foreign agent may serve as adefault router for registered mobile nodes.

RFC2002 defines ‘Care-of Address (COA)’ as the termination point of atunnel toward a mobile node for datagrams forwarded to the mobile nodewhile it is away from home. The protocol can use two different types ofa care-of address: ‘a foreign agent care-of address’ is an addressannounced by a foreign agent with which the mobile node is registered,and ‘a co-located care-of address’ is an externally obtained localaddress which the mobile node has acquired in the network. An MN mayhave several COAs at the same time. An MN's COA is registered with itsHA. The list of COAs is updated when the mobile node receivesadvertisements from foreign agents. If an advertisement expires, itsentry or entries should be deleted from the list. One foreign agent canprovide more than one COA in its advertisements. ‘Mobility Binding’ isthe association of a home address with a care-of address, along with theremaining lifetime of that association. An MN registers its COA with itsHA by sending a Registration Request. The HA replies with a RegistrationReply and retains a binding for the MN.

A single generic mobility handling mechanism that allows roaming betweenall types of access networks would allow the user to conveniently movebetween fixed and mobile networks, between public and private networksas well as between PLMN's with different access technologies. Therefore,mechanisms supporting the Mobile IP functionality are also beingdeveloped in mobile communication systems, such as UMTS and GPRS.

The aim is to implement the Mobile IP as an overlay of the UMTS/GPRSnetwork while maintaining backwards compatibility with present systems,assuming minimal modifications in the GPRS standards and on networkswhose operators do not want to support MIP. FIG. 1 illustrates theminimum configuration for a GPRS operator who wishes to offer the mobileIP service. The current GPRS structure is kept and handles mobilitywithin the PLMN, while MIP allows a user to roam between other systems,such as LANs, and UMTS without loosing an ongoing session. In FIG. 1 theforeign agents FA are located at the GGSNs. All GGSNs may not have FAs.The SGSN and the GGSN may also be co-located. One FA in a PLMN issufficient for offering the MIP service, but for capacity and efficiencyreasons, more than one may be desired. This means that the MS mustrequest a PDP context to be set up with a GGSN that offers FAfunctionality. While setting up the PDP context, the MS is informedabout network parameters of the FA, e.g. care-of address.

The MS may have the same care-of address COA during a session, i.e. aslong as a PDP context is activated. A very mobile MS might performseveral inter-SGSN HOs during a long session, which may cause aninefficient routing. As an initial improvement, a streamlining procedurewith a temporary anchoring point in the GGSN could be introduced: If theMN is not transferring data or is possibly even in the active statewhile moving from one SGSN to another, a new PDP context can be setupbetween the new SGSN and its associated GGSN at the handover. The MNwill get a new care-of address. If the MN is transferring data, e.g.being involved in a TCP session, the MN will move from the old SGSN tothe new one while keeping the PDP Context in the old (anchor) GGSN forthe duration of the data transfer. Once the data transfer is terminated,the PDP Context can be moved to the GGSN associated with the new SGSN.In other words, a new virtual connection to a new GGSN and an associatedFA is established. A typical feature of the mobility agent in the mobileIP is that it periodically transmits agent advertisement messages to themobile nodes in order to advertise its services. The mobile nodes usethese advertisements to determine the current point of attachment to theInternet. Because of the new connection established by the access nodeto the new mobility agent, the agent advertisement messages sent by thenew mobility agent can be received by the mobile node, and thereby themobile node is able to detect the change of the attachment point (i.e.mobility agent) and to initiate a standard mobile IP registration.

More generally, in any Mobile IP agent registration, a PDP context isfirst opened. Then the agent registration is made over the open PDPcontext.

The problem is that because the mobile IP signaling is transferred onthe user plane, the underlying access network nodes, such as the RNC andthe SGSN, have no possibility to know whether the registration wassuccessful or not. Thus, if the agent registration procedure fails, theunderlying infrastructure is totally ignorant of the failure. Thiscauses the unused PDP context to remain open and to use the resourcesunnecessarily. In the inter-GGSN (or inter-FA) handover described above,an additional problem arises. When the handover is performed, the SGSNcontrolling the handover has no possibility of knowing when to close theconnection (PDP context) to the old GGSN/FA.

Similar problems may be encountered in any mobility management on asystem level overlaying the access network. These various overlayingmobility managements are commonly referred to herein as a macro mobilitymanagement.

DISCLOSURE OF THE INVENTION

An object of the present invention is to overcome or alleviate theproblems described above.

The object is achieved by a method and a system which are characterizedby what is disclosed in the attached independent claims. Preferredembodiments of the invention are disclosed in the attached dependentclaims.

In the present invention the gateway node having the associated(integrated) mobility entity is arranged to monitor the macro mobilityregistration during an initial registration or during a handover, and totrigger a deletion of any access network protocol context which is nolonger necessary on the basis of the result of the registration. Forexample, the access network protocol context may be deleted, if theregistration irrecoverably fails. If the registration was unsuccessfulbut a retry could be successful (the first failure was due to a loadsituation, for example), the PDP context may not deleted, but theregistration is retried. A mobility entity may be any entity whichprovides a point of attachment on the macro mobility level, such as amobility agent in mobile IP-type mobility management. In the preferredembodiment of the invention, the macro mobility management is mobileIP-type mobility management.

The present invention avoids the unnecessary use of access networkresources after a failed macro mobility registration. It also has theadvantage of reduced signaling in comparison with a case where a mobilenode/station first deletes the mobile IP entities and then the PDPcontexts some time after the failed registration.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail bymeans of preferred embodiments with reference to the accompanyingdrawings, in which

FIG. 1 illustrates a GPRS network architecture, and

FIG. 2 is a signaling diagram illustrating the method according to theinvention,

FIG. 3 is a flow diagram illustrating the inventive functionality at theGGSN and the SGSN, and

FIG. 4 is a block diagram illustrating the functional blocks of the GGSNinvolved in the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention can be applied to any communications requiringmacro mobility management which overlays the mobility management of anaccess network. The invention is especially well suited for supportingmobile IP-type mobility management in an access network. The accessnetwork may be any access network, such as a radio access network. Theinvention is preferably used for providing a general packet radioservice GPRS in the pan-European digital mobile communications systemGSM (Global System for Mobile Communication) or in corresponding mobilecommunications systems, such as DCS1800 and PCS (Personal CommunicationSystem), or in third generation (3G) mobile systems, such as UMTS,implementing a GPRS-type packet radio. In the following, the preferredembodiments of the invention will be described by means of a GPRS packetradio network formed by the GPRS service and the 3G or GSM systemwithout limiting the invention to this particular access system.

A GPRS architecture utilizing a 3G radio access (such as UMTS) or a 2Gradio access (such as GSM) is illustrated in FIG. 1. The GPRSinfrastructure comprises support nodes such as a GPRS gateway supportnode (GGSN) and a GPRS serving support node (SGSN). The main functionsof the GGSN nodes involve interaction with the external data network.The GGSN updates the location directory using routing informationsupplied by the SGSNs about an MS's path and routes the external datanetwork protocol packet encapsulated over the GPRS backbone to the SGSNcurrently serving the MS. It also decapsulates and forwards externaldata network packets to the appropriate data network and handles thebilling of data traffic.

The main functions of the SGSN are to detect new GPRS mobile stations inits service area, handle the process of registering the new MSs alongwith the GPRS registers, send/receive data packets to/from the GPRS MS,and keep a record of the location of the MSs inside its service area.The subscription information is stored in a GPRS register (HLR) wherethe mapping between a mobile's identity (such as MS-ISDN or IMSI) andthe PSPDN address is stored. The GPRS register acts as a database fromwhich the SGSNs can ask whether a new MS in its area is allowed to jointhe GPRS network.

The GPRS gateway support nodes GGSN connect an operator's GPRS networkto external systems, such as other operators' GPRS systems, datanetworks 11, such as an IP network (Internet) or an X.25 network, andservice centres. Fixed hosts 14 can be connected to the data network 11e.g. by means of a local area network LAN and a router 15. A bordergateway BG provides access to an inter-operator GPRS backbone network12. The GGSN may also be connected directly to a private corporatenetwork or a host. The GGSN includes GPRS subscribers' PDP addresses androuting information, i.e. SGSN addresses. Routing information is usedfor tunneling protocol data units PDU from the data network 11 to thecurrent switching point of the MS, i.e. to the serving SGSN. Thefunctionalities of the SGSN and GGSN can be connected to the samephysical node (SGSN+GGSN).

The home location register HLR of the GSM network contains GPRSsubscriber data and routing information and it maps the subscriber'sIMSI into one or more pairs of the PDP type and PDP address. The HLRalso maps each PDP type and PDP address pair into a GGSN node. The SGSNhas a Gr interface to the HLR (a direct signaling connection or via aninternal backbone network 13). The HLR of a roaming MS and its servingSGSN may be in different mobile communication networks.

The intra-operator backbone network 13 which interconnects an operator'sSGSN and GGSN equipment can be implemented, for example, by means of alocal network, such as an IP network. It should be noted that anoperator's GPRS network can also be implemented without theintra-operator backbone network, e.g. by providing all features in onecomputer.

Network access is the means by which a user is connected to atelecommunications network in order to use the services and/orfacilities of that network. An access protocol is a defined set ofprocedures that enables the user to employ the services and/orfacilities of the network. The SGSN, which is at the same hierarchicallevel as the mobile switching centre MSC, keeps track of the individualMS's location and performs security functions and access control. TheGPRS security functionality is equivalent to the existing GSM security.The SGSN performs authentication and cipher setting procedures based onthe same algorithms, keys, and criteria as in the existing GSM. The GPRSuses a ciphering algorithm optimized for packet data transmission.

In order to access the GPRS services, an MS shall first make itspresence known to the network by performing a GPRS attach. Thisoperation establishes a logical link between the MS and the SGSN, andmakes the MS available for SMS over the GPRS, paging via the SGSN, andnotification of incoming GPRS data. More particularly, when the MSattaches to the GPRS network, i.e. in a GPRS attach procedure, the SGSNcreates a mobility management context (MM context), and a logical linkLLC (Logical Link Control) is established between the MS and the SGSN ona protocol layer. MM contexts are stored in the SGSN and MS. The MMcontext of the SGSN may contain subscriber data, such as thesubscriber's IMSI, TLLI and location and routing information.

In order to send and receive GPRS data, the MS shall activate the packetdata address that it wants to use, by requesting a PDP activationprocedure. This operation makes the MS known in the corresponding GGSN,and interworking with external data networks can commence. Moreparticularly, one or more PDP context is created in the MS and the GGSNand the SGSN, and stored in the serving SGSN with the MM context. ThePDP context defines different data transmission parameters, such as thePDP type (e.g. X.25 or IP), PDP address (e.g. IP address), quality ofservice QoS and NSAPI (Network Service Access Point Identifier). The MSactivates the PDU context with a specific message, Activate PDP ContextRequest, in which it gives information on the TLLI, PDP type, PDPaddress, required QoS and NSAPI, and optionally the access point nameAPN. The SGSN sends a create PDP context message to the GGSN whichcreates the PDP context and sends it to the SGSN. The SGSN sends the PDPcontext to the MS in an Activate PDP Context Response message, and avirtual connection or link between the MS and the GGSN is established.As a result, the SGSN forwards all the data packets from the MS to theGGSN, and the GGSN forwards the SGSN all data packets received from theexternal network and addressed to the MS. The PDP context is stored inthe MS, the SGSN and the GGSN. When the MS roams to the area of a newSGSN, the new SGSN requests the MM and PDP contexts from the old SGSN.

FIG. 1 illustrates the implementation of a mobile IP in the GPRS/3Genvironment.

The MS can be a laptop computer PC connected to a packet radio-enabledcellular telephone. Alternatively, the MS can be an integratedcombination of a small computer and a packet radio telephone, similar inappearance to the Nokia Communicator 9000 series. Yet furtherembodiments of the MS are various pagers, remote-control, surveillanceand/or data-acquisition devices, etc. The user of a mobile station MSsubscribes to a special Mobile IP service. The subscription informationis stored in the Home Location Register HLR together with the user'shome IP address.

In FIG. 1 the foreign agents FA are located at (integrated into) theGGSNs. An alternative is that the SGSN and the GGSN are co-located, andthe FAs are located at the SGSN+GGSNs. The present invention isapplicable in both cases. It should be noted that there may be more thanone SGSN and GGSN in one network. All GGSNs may not have FAs. Each FAhas an IP address on the Internet and in the operator's own privateGPRS/3G backbone network. More precisely, the FA's IP address is suchthat IP packets destined to that address are routed on the Internet tothe GGSN associated with the FA. When the MN leaves its home subnet andregisters to a new FA, it can no longer be reached on the basis of itshome IP address alone, but must be assigned an address belonging to thevisited network, called the care-of address (COA). The care-of addresspositively identifies the instantaneous location of the mobile terminaland may be: 1) the IP address of the FA belonging to the visitednetwork, or 2) an IP address acquired directly by the mobile terminalthrough an autoconfiguration mechanism from the local IP address space,in which case the term co-located care-of address is used. Whenregistering to a new FA and obtaining a COA, the MN which then registerswith a home agent HA, in its home network, and informs the latter of itsCOA. In FIG. 1 a home agent HA is located in a data network 11 which isthe home network of the mobile node MN associated with the mobilestation MS. A second host 14 wishing to communicate with the MN need notbe aware that the MN has moved: it simply sends IP packets addressed tothe MN's home IP address. These packets are routed via normal IP routingto the MN's home network, where they are intercepted by the HA. The HAencapsulates each packet of this kind in another IP packet whichcontains the MN's COA and these packets are then delivered to the FA (aprocess called tunneling). The FA forwards the IP packet to the GGSN.The GGSN forwards the IP packet (which may be encapsulated fortransmission over the GPRS backbone) to the serving SGSN which furtherforwards the IP packet to the MS/MN. Packets from the MN to another host14 need not necessarily be tunneled: the MN may simply send them to theGGSN which directly forwards the packets to the second host 14 withoutinterception by the FA or the HA.

An example of inter-GGSN handover will be now described with referenceto FIG. 2.

Reference is now made to FIG. 1. The home network of the mobile stationMS is the GPRS/3G network 1. The user of the mobile station MSsubscribes to a special mobile IP service, and an IP application in theMS or in a separate data terminal is a mobile node MN in a mobile IPcommunication. It is assumed that the MS/MN is attached to the homenetwork 1 and the radio access network RAN1 (PS1 and PSC/RNC1). Aserving support node in the home network is SGSN1. MM and PDP contextshave been created for the mobile IP service as described above, and avirtual connection is provided between the MS/MN and SGSN1 as well asbetween the SGSN1 and a gateway node GGSN1 which has an associatedforeign agent FA1. Thus, the IP packets addressed to the MN can beforwarded to the MN over the home network 1 and RAN1. The COA of the MNhas been registered to the home agent HA in the home network 11 of theMN, so that mobile IP tunneling is provided from the HA to the GGSN/FA1.

Let us now assume that the MS/MN moves to the service area of anotherGPRS/3G network 2 which is served by a support node SGSN2. When theMS/MN arrives at a new RAN2, the MS part listens to radio broadcastmessages, which contain information about radio parameters, network andcell identity, etc. as well as information about available core network,service providers, service capabilities, etc. On the basis of thebroadcast, the MS determines that the network and/or the routing areahas changed. Upon detecting a change of routing area, the MS/MN sends arouting area update request to the new SGSN, namely SGSN2, as shown inFIG. 2. The new SGSN2 sends an SGSN context request message to the oldSGSN1 (in step 2) to get the MN and PDP contexts for the MS/MN. The oldSGSN1 replies with an SGSN context response message which contains theMN and PDP contexts (step 3). According to the preferred embodiment ofthe invention, the information transferred from the old access node tothe access node may be provided with an information field whichindicates the different types of the PDP contexts, or at least theMobile IP-related PDP contexts. This allows the SGSN to distinguish theMobile IP-dedicated PDP contexts from other active PDP contexts of themobile station which should not be involved in the change of themobility agent. There are various possible ways to implement the PDPcontext type information. For example, a PDP Context Information Elementwhich is carried in the SGSN Context Response message in the GPRS (andin the forward SNRC relocation message in UMTS) may be provided with afield indicating the type of service used over the PDP context. The typefield may contain an Access Point Name which has a value indicating aMobile IP PDP context. Spare bits in the PDP Context Information Elementmay be used for the new field, or alternatively the new field may be anextension of the current PDP Context Information Element format. Itshould be noted, however, that the exact implementation is not relevantto the invention. It is only relevant, in this specific embodiment thatthe information received from the old SGSN enables the new SGSN todetermine which PDP context(s) is (are) dedicated to the Mobile IP.

In step 4, the new SGSN2 may, in certain situations, executeauthentication/security functions which may involve an interrogation ofthe HLR of the MS/MN. If the user has at least one activated PDPcontext, the new SGSN2 sends a SGSN context acknowledge message to theold SGSN1. The old SGSN1 may now start forwarding of buffered datapackets belonging to the activated PDP context, if any, to the newSGSN2. The new SGSN2 now detects that the new foreign agent FA2 shouldpreferably be used instead of FA1, in step 6. The SGSN2 deletes the PDPcontext from the old GGSN/FA1 by sending a delete PDP context request tothe old GGSN/FA1. As a result, any active PDP context in the GGSN/FA1 isdeactivated, and the GGSN/FA1 acknowledges by sending a delete PDPcontext response to the new SGSN2 (step 8 in FIG. 2). Referring to FIG.3, the process proceeds to step 34 wherein the new SGSN2 creates a PDPcontext in the GGSN/FA2 by sending a create PDP context request to thenew GGSN/FA2 (step 9 in FIG. 2). The GGSN/FA2 creates the PDP contextfor the MS/MN and returns a create PDP context response to the new SGSN2(step 10 in FIG. 2). The new SGSN2 establishes MN and PDP context forthe MS/MN, and replies to the MS/MN with a routing area update acceptmessage (step 11). The MS/MN acknowledges with a routing area updatecomplete message (step 12). A virtual connection has thus beenestablished between the MS/MN and the GGSN/FA2.

All the previous procedures have been executed on the GPRS/3G layeronly. Due to the newly established connection to the GGSN/FA2, the MN isable to hear the agent advertisement messages broadcasted by the new FA2in accordance with the mobile IP protocol. Upon receiving an agentadvertisement from the new FA2, the MN is able to detect a change in thepoint of attachment, i.e. a change of the FA, in accordance with the MIPstandard. The agent advertisement message may also include the care-ofaddress COA, or the MN may acquire the COA in accordance with the MIPstandard. Then the mobile node MN registers its COA with its home agentHA in accordance with the MIP standard (step 14 in FIG. 2). Depending onits method of attachment, the MN will register either directly to itsHA, or through the new FA which forwards the registration to the HA.Thereafter, mobile IP tunneling between the HA and the old GGSN/FA1 isreleased and new mobile IP tunneling is established between the HA andthe new GGSN/FA2, in accordance with the mobile procedures.

As the mobile IP signaling is transferred on the user plane, theunderlying access network nodes, such as the RNC and the SGSN, have nopossibility of knowing whether the registration was successful or not.

According to the present invention, the GGSN2 monitors (step 15) whetherthe Mobile IP registration is successful or fails. This is possiblesince the FA2 is located at the GGSN2, and, therefore, the GGSN2 alsoknows the status of the FA2. When the GGSN2 detects that theregistration was successful, no further measures are required exceptthat the old connection between the GGSN1 and SGSN2 must be deleted.However, if the GGSN2 detects that the registration fails, the GGSN2 candetermine the severity of the failure and decide whether to allow themobile node MN to try to register again or to terminate the registrationprocedure and delete the PDP context. If the GGSN decides that theregistration can be tried again, the PDP context is maintained. If theGGSN2 decides that the failure is so severe that no repetition of theregistration procedure can be allowed in order to complete theregistration, the GGSN2 deletes the associated PDP context at the GGSN2(step 16) and sends to the SGSN2 a Delete PDP message (step 17). Themessage may also include a cause value which indicates why the deletionwas made, i.e. failure in the MIP registration. The SGSN2 receives themessage and deletes the PDP context to the GGSN2 (step 18). The SGSN2may also use the cause value in the message in deciding (step 19)whether the other PDP context open to the old GGSN1 (assuming steps 7and 8 have not yet been performed) should be maintained or deleted, orshould the Air PDP context to the MS/MN be also deleted. If the PDPcontext to the old GGSN1 is maintained, the MS/MN is able to reregisterto the FA1 and/or to continue communication. To enable this alternative,the deletion of the old PDP context, i.e. steps 7 and 8, is delayed longenough that a possible Delete PDP message from the GGSN2 due to a failedregistration will be received before the deletion. In step 20, the SGSN2sends Delete PDP Request messages to the MS and GGSN1, upon decidingthat the PDP contexts are to be deleted both from the MS and GGSN1.

The principles described above are applicable to any situation in whichan MIP registration is attempted. In the GPRS attach procedure, the MSrequests a PDP activation for a mobile IP by an Activate PDP ContextRequest message. The SGSN2 sends a Create PDP Context message to theGGSN2 which creates the PDP context and sends it to the SGSN2. The SGSN2sends the PDP context to the MS in a Activate PDP Context Responsemessage. Thus, a PDP context is created in the MS and the GGSN2 and theSGSN2 and a virtual connection or link between the MS and the GGSN2/FA2is established. As a result, an MIP registration can now be performedover the virtual connection. As described above with respect to FIG. 2,the GGSN2 monitors the Mobile IP registration procedure and deletes thePDP context and releases the virtual connection, if the registrationfails.

FIG. 3 is a flow diagram illustrating the inventive functionality at theGGSN and the SGSN. First, in step 31 a PDP context and a new connectionis created. Then a MIP registration is attempted over a new connection(step 32). The GGSN monitors the registration (step 33) and determineswhether the registration was successful or not (step 34). If theregistration was successful, the GGSN determines whether there are otherMIP-PDP contexts for the mobile node MN (step 42). If not, the procedureis ended. If there is another MIP-PDP context which is unnecessary forthe new registration, the unnecessary PDP context is deleted (step 43)and the procedure is ended.

If it is determined, however, in step 34 that the registration failed,it is then determined whether it is possible to retry the registration(step 35). If yes, the registration is retried (step 36) and theprocedure returns to step 33. If retry is not possible, the PDP contextis deleted at the GGSN and a deleted PDP context message with a causevalue is sent to the SGSN (step 37). The SGSN determines whether thereare other PDP contexts for the same MN (step 38). If not, the connectionbetween the MN and the old GGSN/FA is deleted (step 41). If any otherPDP contexts exist in step 38, it is checked whether a fallback to thisold PDP context is possible (step 39). If not, the procedure proceeds tostep 41. If a fallback is possible in step 39, the old PDP context tothe old FA and the old FA is used (step 40).

FIG. 4 is a block diagram illustrating the functional blocks of the GGSNinvolved in the present invention. Firstly, a macro mobility managemententity 44, such as the foreign agent FA, is integrated into the GGSN.Further, monitoring means 45 are provided for monitoring the macromobility (MIP) registration. Determining means 46 are provided fordetermining on the basis of the result of the mitered registrationwhether there is at least one unnecessary PDP context. Triggering means47 are responsive to the determining means 46 so as to trigger adeletion of any determined unnecessary PDP context. PDP context deletionmeans stand for any entity or functionality in the system which isrequired for deleting a PDP context.

The description only illustrates preferred embodiments of the invention.The invention is not, however, limited to these examples, but it mayvary within the scope and spirit of the appended claims.

1. A gateway node, configured to monitor a macro mobility registration in an access system which comprises a plurality of mobile nodes, access nodes and a first mobility entity which is associated with said first gateway node and arranged to provide macro mobility management services to the mobile nodes, each mobile node being able to perform a macro mobility registration to the first mobility entity over a respective dedicated access network connection established by opening an access network protocol context at a first access node and the first gateway node, determine in response to detecting a failure in said macro mobility registration whether it is possible to retry the macro mobility registration or whether the registration has irrecoverably failed, and trigger a deletion of any access network protocol context which is no longer necessary on the basis of the result of the registration.
 2. A gateway node as claimed in claim 1, comprising said gateway node being integrated into the same physical node with said access node.
 3. A gateway node, configured to monitor the macro mobility registration in an access system which comprises a plurality of mobile nodes, access nodes and a first mobility entity which is associated with said gateway node and arranged to provide macro mobility management services to the mobile nodes, each mobile node being able to perform a macro mobility registration to the first mobility entity over a respective dedicated access network connection established by opening an access network protocol context at a first access node and the gateway node, and send a context deletion message to the first access node to trigger a deletion of any access network protocol context which is no longer necessary, when the macro mobility registration irrecoverably fails.
 4. A gateway node as claimed in claim 2, comprising said gateway node being integrated into the same physical node with said access node. 